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February 03, 2005

Dawkins reconsiders Out of Africa?

I've read about ~1/3 of Richard Dawkins' The Ancestor's Tale, and I highly recommend it. Dawkins manages to master the constraints of prose aimed at the lay audience (neither florid nor excessively spare & dry) along with a substantive survey of a diverse range of topics, from fossil morphology to molecular phylogenetics (at least so far).

But, I am drawn to something that Dawkins admits rather early on in the book, he favors Alan Templeton's Out of Africa again and again hypothesis. In short, Dawkins is arguing against the dominant model of total replacement that is generally promoted by popularizers who focus on human genetic history. This is important, not because Dawkins is a geneticist or paleontologist, he has no training in these fields (he is an ethologist), rather, with the passing of Stephen Jay Gould he is the premier popularizer of evolutionary ideas and so can shift the public discourse in a fashion that might allow for the emergence of new ideas and an eventual switch in paradigms.1

The model that Dawkins seems to mildly favor gives an important role to Africa as the source of several outmigrations. Nevertheless, it infers from multiple locii that total replacement of non-African hominid genome did not occur, that is, there was a level of interbreeding between African and non-African populations. With persistent suggestions that neutral markers might not be so neutral and the new evidence (and don't forget this) which points to ancient "non-African" alleles in modern populations there might be a coming shake up in the world of paleoanthropology. Dawkins' own interests do not seem to lay specifically in the realm of humanity, instead his promotion of Templeton's hypothesis against popular conventional wisdom seems to be tied to a concern that relying on only a few locii as markers of ancestry might be leading people down the wrong path (the locii usually are on the nonrecombinant Y chromosome and the mtDNA, which chronicle the unbroken male and female lineage). The "gene's eye view" which Dawkins popularized would caution one against this, organisms are vehicles for a collections of genes, and the history of the various polymorphisms of those genes might not present a seamless historical narrative, in other words, one might not always be able to generalize from the NRY and mtDNA to the rest of the genome. This is clear in the case of polymorphic gene complexes like the HLA, which persist across species because of balancing or long term frequency dependent selection. Dawkins notes that if you carefully selected your locii individuals could find themselves more "closely related" to a chimpanzee than near blood relations. One problem, as Dawkins notes repeatedly, is that we confound our common sense conceptions of ancestry with the inheritance and transmission of genes. An individual human has one ancestral tree, various alleles over innumerable locii have specific trees which are not going to be perfectly concordant.

Addendum: In the comments Steve wondered about the contemporary relevance of these paleoanthropological theories...well, I just recalled an important one, it makes the Environment of Evolutionary Adaptedness (EEA) less cut & dry in the context of modern humans. Since about 1990 the "evolutionary psychology" movement promoted by John Toobey and Leda Cosmides has basically assumed Out of Africa as the paleoanthropological backdrop for the EEA, and certainly the developmnent of Human Universals makes sense if you assume that one discrete human population developed its primary tendencies in a particular locale and subsequently radiated in a massive range expansion. A modified Out of Africa model with some localized interbreeding with non-African homonid populations does not refute the empirical reality of the Human Universals, rather, it makes more plausible to some the possible persistance of region specific Evolutionarily Stable Strategies (ESS). I am not one who believes that "there wasn't enough time" for local ESSs to develop after an Out of Africa movement as recent as ~50,000 years ago, but, certainly the possibility of ancient non-African genetic material opens the door for the perpetuation of specialized local adaptations even for those who assert that ~1 million years would be needed for the variegation that some hypothesize.

Related: "Racial Diversity", The Great Leap, Paradigms (and books) lost.... , Erectine harems, Of lice & "men" and Two Wave Model.

1 - I make no claim that Dawkins will directly impact the scientific research in this area in any fashion, rather, his input might be able to reduce the latency between a paradigm shift within the discipline and the spread of such ideas to the general public. Additionally, there might be an indirect effect in that the public readiness for certain ideas, as opposed to others, does seem to influence how scientists present their theories (ie; I find it interesting that both multi-regionalists and Out-of-Africa theorists will imply that the other group's model has racist undertones).

Posted by razib at 01:29 AM